This diagram gives the suggested cable pinouts for IBM PC/XT, PC/AT, and compatible computers
Printer
end of
cable
25-Pin M
CPU XT
end of
cable
25-Pin F
Printer
end of
cable
25-Pin F
CPU AT
end of
cable
9-Pin F
Gnd 1 1 Gnd 1
RXD 2 2 RXD RXD 2 2 RXD
TXD 3 3 TXD TXD 3 3 TXD
DTR 4 4 DTR DSR 6 4 DTR
DSR 5 5 DSR CTS 5 5 GND
GND 6 6 GND GND 7 7 RTS
RTS 8 8 RTS DTR 20 6 DSR
CTS 20 20 CTS RTS 4 8 CTS
SG 7 7 SG 9